Two methods are known for rendering elevation information in a display generated from an electronic map, namely (i) isolines (also called contour lines) representing points of the same elevation, and (ii) shading of the map colour to represent elevation information. While isolines may provide an accurate representation of elevation, isolines can clutter the map display and are not intuitive to all users. Map clutter may be a particular problem when displaying the map on a relatively small electronic display device, or when it is also desired to display other map information such as navigation and location information. Shading can provide a more intuitive representation of elevation information without cluttering the display. As used herein, the term “shading” means applying a darkening and/or lightening of the map colour, akin to a positive or negative shadow.
Referring to FIG. 1, a conventional technique for shading is to include the shading as a static feature of the map colour in the digital map. A digital map 12 is generated by processing map source information 10 that includes elevation data, to create the shading as a static template within the background colour in the digital map 12. To display the digital map 12, a rendering process 14 is used to generate an image 18 including the fixed elevation shading template at a desired display scale represented by a display scale input 16.
In devising the present invention, it has been appreciated that the above technique lacks considerable finesse in being able to adapt to displaying the map at different viewing scales or zoom levels. The shading is fixed as part of the digital map 12, and is not adaptive. The shading pattern also depends on the specific shading technique used when creating the digital map 12. Different shading techniques create different shading patterns based on the same elevation data. While a certain shading technique may be suited to displaying the map at a certain display scale, generating a display at other display scales can require interpolation or averaging of the shading pattern. This can create severe inaccuracies in the elevation shading. For example, as the display scale is varied, peaks and valleys in the elevation may appear to change shape and location as a result of averaging or interpolation inaccuracies.
The present invention has been devised bearing the above problems in mind.